Large-diameter pipe-pulling back-dragging resistance prediction and resistance reduction construction method

Abstract

The application provides a large-diameter pipe-pulling back-dragging resistance prediction and resistance reduction construction method, comprising the following steps: collecting stratum parameters, large-diameter pipe parameters and construction process parameters of a pipe-pulling construction area; calculating resistance values of a back-dragging whole process under different construction conditions by using a multi-mechanical coupling model; determining a resistance reduction construction scheme in combination with stratum characteristics, pipe material and construction environment of the construction area according to the resistance values of the back-dragging whole process under different construction conditions; monitoring resistance changes of the back-dragging in real time in the whole process, and dynamically adjusting construction parameters according to monitoring data; and after the construction is completed, performing comprehensive detection and acceptance according to preset acceptance standards. The application can effectively improve the safety, economy and construction quality of large-diameter pipe-pulling construction, and reduce back-dragging risks by accurately predicting back-dragging resistance through a multi-mechanical coupling model, determining a resistance reduction scheme in combination with multiple factors, dynamically adjusting construction parameters in real time and completing comprehensive acceptance.

Description

Technical Field

[0001] This invention belongs to the field of trenchless pipe pulling technology, and more specifically, it relates to a method for predicting and reducing the drag resistance of large-diameter pipe pulling. Background Technology

[0002] With the accelerating pace of urbanization and the continuous increase in investment in urban infrastructure construction, underground pipelines, as a crucial component of urban infrastructure, undertake vital functions such as water supply and drainage, gas transmission, power transmission, and communication. Their construction quality and efficiency directly impact the normal operation of the city and the quality of life for residents. Trenchless pipe laying technology, as a novel underground pipeline laying technology, offers advantages over traditional open-cut construction methods, including less damage to surface facilities, shorter construction cycles, significant environmental benefits, relatively lower construction costs, and strong adaptability to complex construction environments. It is widely used in underground pipeline laying projects across various fields such as municipal engineering, gas, water supply and drainage, power, and communications. Among these, large-diameter pipe laying (diameter ≥ 800mm) plays an irreplaceable role in urban trunk pipeline construction, long-distance pipeline laying, and large-scale engineering supporting pipeline projects due to its outstanding advantages such as large flow capacity, strong load-bearing capacity, and wide applicability. It is particularly suitable for densely populated, busy, and densely built-up urban centers, effectively avoiding the damage to surface traffic, surrounding buildings, and existing underground pipelines caused by traditional open-cut construction, reducing dust and noise pollution during construction, and minimizing the impact of construction on the normal operation of the city.

[0003] However, large-diameter pipe pulling faces a series of technical challenges during the pullback process, including high resistance, complex resistance distribution, and difficulty in prediction. These challenges have become key factors restricting construction efficiency, quality, and safety. Compared to small-diameter pipe pulling, large-diameter pipes are heavier and have a wider contact area with the borehole wall. During pullback, they are subjected to the coupling effects of multiple forces, mainly including ground friction resistance, borehole fluid drag resistance, pipe end face resistance, and additional resistance in bending sections. These resistances are superimposed, resulting in a pullback resistance of much greater for large-diameter pipes than for small-diameter pipes. If the pullback resistance cannot be accurately predicted, improper selection of the pipe pulling machine (such as insufficient pulling force or overload) can easily lead to pipe overload, resulting in pipe damage, deformation, pipe pulling failure, borehole wall collapse, and other safety accidents. This not only significantly increases construction costs and prolongs the construction period but may also cause secondary damage to the surrounding environment and existing underground pipelines, leading to safety hazards and economic losses.

[0004] Currently, there are many existing methods for predicting the pullback resistance of pipe pulling, but most of them have obvious defects and shortcomings, making it difficult to meet the actual construction needs of large-diameter pipe pulling. On the one hand, existing prediction formulas are too general and simplistic, often using simple weighted algorithms, failing to fully consider the multi-mechanical coupling effects during the pullback process, and also failing to comprehensively consider the influence of various factors such as different formation types, construction parameters, hole-forming fluid types, and pipe bending angles on the pullback resistance. This results in a large deviation between the predicted value and the actual resistance value during construction, typically exceeding 20%, making it impossible to provide reliable guidance for pipe pulling machine selection, construction parameter design, and construction safety control. For example, some existing technologies only consider the frictional resistance of the formation and the resistance at the pipe end, ignoring the drag resistance of the drilling fluid and the additional resistance of the bending section. However, for large-diameter pipe pulling, these two resistances can account for 30% to 40% of the total pullback resistance. Ignoring these two resistances will lead to serious distortion of the prediction results, which in turn will lead to construction decision errors and increase construction risks. In addition, the prediction formulas of some technologies are vague and have no clear numerical range. The parameter values ​​are arbitrary and cannot be accurately calculated in combination with specific engineering scenarios. They are not practical and are difficult to promote and apply in on-site construction.

[0005] In terms of drag reduction construction, existing technologies also have many shortcomings and defects, failing to meet the drag reduction requirements of large-diameter pipe drawing. Existing drag reduction construction methods are not targeted enough, mostly employing single drag reduction measures, such as using only hole-forming fluid lubrication or simple pipe surface treatment, without forming a systematic and coordinated drag reduction system. This results in unstable drag reduction effects, with drag reduction rates generally below 10%, failing to effectively reduce the pullback resistance of large-diameter pipe drawing. For example, using ordinary drilling mud for drag reduction in cohesive soil layers can easily lead to problems such as insufficient mud viscosity, poor mud film formation, borehole diameter reduction, and mud adhesion to the pipe, which can actually increase the frictional resistance between the pipe and the borehole wall. In sandy soil layers, the lack of specialized foamed drilling mud cannot effectively reduce the drag resistance of the forming fluid on the pipe, and it is also difficult to ensure the stability of the borehole wall, which can easily lead to borehole wall collapse and thus increase pullback resistance. In addition, the existing construction process lacks a sound dynamic control mechanism, which cannot adjust the construction parameters in a timely manner according to the real-time changes in pullback resistance. When the resistance suddenly increases, it is impossible to take effective drag reduction measures quickly, which can easily lead to construction accidents such as pipe pulling machine overload and pipe damage, which does not meet the safety and efficiency requirements of actual engineering construction. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a method for predicting and reducing the drag resistance of large-diameter pipe pullback.

[0007] A method for predicting and reducing drag during the pullback of large-diameter pipes includes:

[0008] Step 1: Collect geological parameters, large-diameter pipe parameters, and construction process parameters for the pipe pulling construction area;

[0009] Step 2: Calculate the resistance values ​​of the entire pullback process under different construction conditions using a multi-mechanism coupling model;

[0010] Step 3: Determine the drag reduction construction plan based on the resistance value of the entire pullback process under different construction conditions, combined with the geological characteristics of the construction area, pipeline material and construction environment;

[0011] Step 4: Monitor the changes in pullback resistance in real time throughout the entire pullback process, and dynamically adjust the construction parameters based on the monitoring data;

[0012] Step 5: After construction is completed, conduct a comprehensive inspection and acceptance according to the preset acceptance standards.

[0013] Preferably, in step 2, the formula for calculating the total pullback resistance during the entire pullback process is:

[0014]

[0015] in, For total pullback resistance; This refers to the frictional resistance between the pipe inside the borehole and the formation. The drag resistance generated by the pore-forming fluid on the pipe surface. For the resistance at the pipe end; Additional resistance generated by the curved section of the pipeline.

[0016] Preferably, in step 2, when the construction area is a cohesive soil layer, the formula is used:

[0017]

[0018] Calculate the frictional resistance between the pipe inside the borehole and the formation; where, This indicates the frictional resistance between the pipe inside the borehole and the soil layer when the construction area is a cohesive soil layer. Here, y represents the coefficient of friction between the pipeline and the soil layer, H is the pipeline burial depth, and y is the groundwater level depth. denoted as the coefficient of earth pressure at rest, c as the cohesion, φ as the angle of internal friction, e as the void ratio, D as the outer diameter of the pipe, and L as the length of the pipe.

[0019] When the construction area is a sandy soil layer, the formula is used:

[0020]

[0021] Calculate the frictional resistance between the pipe inside the borehole and the formation; where, This indicates the frictional resistance between the pipe inside the borehole and the stratum when the construction area is a sandy soil layer. γ is the friction coefficient between the pipeline and the stratum in the sandy soil layer, γ is the unit weight of the stratum, and k is the permeability coefficient.

[0022] Preferably, in step 2, when using mud-type drilling fluid during construction, the formula is:

[0023]

[0024] Calculate the drag resistance generated by the pore-forming fluid on the pipe surface; where, This refers to the drag resistance exerted by the drilling fluid on the pipe surface when using mud-based drilling fluid during construction. This is the drag coefficient. The density of the pore-forming fluid. For the pullback speed, The viscosity of the pore-forming fluid;

[0025] When using foam-type hole-forming fluid during construction, the formula is as follows:

[0026]

[0027] Calculate the drag resistance generated by the pore-forming fluid on the pipe surface; where, This indicates the drag resistance that the foam-type pore-forming fluid generates on the pipe surface when used during construction. The diameter of the bubble in the foam-forming liquid is denoted as .

[0028] Preferably, in step 2, the formula for calculating the pipe end face resistance is:

[0029]

[0030] in, Indicates the resistance at the pipe end. The diameter of the enlarged hole.

[0031] Preferably, in step 2, when the pipe bend angle For angles ≤15°, a linear calculation formula is used:

[0032]

[0033] Calculate the additional resistance generated by the pipe section with a small-angle bend; where, This indicates the additional resistance generated by the small-angle bend in the pipe. This indicates the total pullback resistance. Indicates the radius of curvature of the curved segment. Indicates the specific gravity of the pore-forming fluid;

[0034] Bending angle For angles >15°, a nonlinear calculation formula is used:

[0035]

[0036] Calculate the additional resistance generated by the pipe section with a large-angle bend; among which, This indicates the additional resistance generated by the pipe section with a large angle bend.

[0037] Preferably, when there are multiple layers of different geological strata in the pipe pulling construction area, the entire pipeline is divided into several sections according to the geological distribution. Each section corresponds to a different geological stratum type. The division principle is based on the burial depth and soil type differences. Each section is at least 20m long, ensuring that the geological characteristics of each section are uniform. The resistance of each section is calculated separately, and then the resistance values ​​of all sections are summed to obtain the total pullback resistance of the entire pipeline pullback process. The calculation formula is as follows:

[0038]

[0039] Where n is the number of pipe segments. Let be the frictional resistance of the i-th segment of the pipe. Let be the drag resistance of the i-th segment of the pipe. Let be the pipe end frontal resistance of the i-th segment of the pipe. Add resistance to the curved section of the i-th pipe segment.

[0040] Preferably, in step 3, the drag reduction construction scheme includes: drag reduction through optimized poring fluid, drag reduction through pipe surface modification, drag reduction through graded pore enlargement, and dynamic drag reduction control; wherein, the drag reduction process through optimized poring fluid is as follows: for cohesive soil layers, the poring fluid is changed to bentonite slurry, and its ratio is: bentonite:water:soda ash:polyacrylamide = (15~25):100:(0.3~0.8):(0.1~0.3); for sandy soil layers, the poring fluid is changed to foamed bentonite slurry, and its ratio is: bentonite:water:foaming agent:viscosity enhancer = (10~18):100:(1.5~3.0):(0.2~0.5);

[0041] The process of modifying and reducing drag on the pipe surface is as follows: a polytetrafluoroethylene modified drag-reducing coating is uniformly applied to the outer surface of the pipe, and a flexible sealing sleeve is used to wrap the pipe joint.

[0042] The staged reaming optimization and drag reduction process is as follows: the diameter of the first stage reaming is controlled at 1.2 to 1.3 times the outer diameter of the pipe, the diameter of each stage reaming increases by 0.1 to 0.2 times the outer diameter of the pipe, and the final reaming diameter is controlled at 1.3 to 1.5 times the outer diameter of the pipe. The reaming speed is controlled at 1.0 to 2.0 m / min, and after each stage of reaming is completed, the hole is flushed with pore-forming fluid for 30 to 60 minutes.

[0043] The dynamic drag reduction control process is as follows: when the total drag resistance reaches the preset threshold, the drag speed is adjusted to 0.3~1.0m / min, the pore-forming fluid circulation flow rate is increased to 1.8~2.5m / s, and drag-reducing agent is added.

[0044] Preferably, in step 4, when the deviation between the actual resistance value and the calculated total pullback resistance is ≤10%, the adjustment range is 5%~10% of the original parameter; when the deviation value is >10%, the adjustment range is 10%~20% of the original parameter, so that the resistance value is controlled within the preset threshold.

[0045] This invention also provides a large-diameter pipe pullback resistance prediction and drag reduction construction system, comprising:

[0046] The parameter acquisition module is used to collect geological parameters, large-diameter pipe parameters, and construction process parameters in the pipe pulling construction area.

[0047] The resistance calculation module is used to calculate the resistance value of the entire pullback process under different construction conditions using a multi-mechanical coupling model;

[0048] The drag reduction construction scheme determination module is used to determine the drag reduction construction scheme based on the resistance value of the entire pullback process under different construction conditions, combined with the geological characteristics of the construction area, pipeline material and construction environment.

[0049] The construction parameter adjustment module is used to monitor the changes in pullback resistance in real time throughout the entire pullback process and dynamically adjust the construction parameters based on the monitoring data.

[0050] The inspection and acceptance module is used to conduct comprehensive inspection and acceptance according to preset acceptance standards after construction is completed.

[0051] The beneficial effects of the large-diameter pipe pulling resistance prediction and drag reduction construction method provided by this invention are as follows: Compared with the prior art, this invention adopts four core drag reduction measures: hole-forming fluid optimization, pipe surface modification, staged hole expansion, and dynamic control, forming a systematic and synergistic drag reduction system. It is designed specifically according to the site geological characteristics, pipe material, and construction environment to achieve "one solution for one site". The drag reduction rate reaches 15%~40%, significantly reducing pullback resistance, effectively avoiding construction accidents such as pipe pulling machine overload, pipe damage, and hole wall collapse, improving construction efficiency, shortening the construction period, and reducing construction costs.

[0052] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0053] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 The flowchart illustrates a method for predicting and reducing drag during the pullback of large-diameter pipes, as provided in an embodiment of the present invention. Detailed Implementation

[0055] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0056] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0057] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0058] Please see Figure 1 A method for predicting and reducing drag during the pullback of large-diameter pipes, comprising:

[0059] Step 1: Collect geological parameters, large-diameter pipe parameters, and construction process parameters for the pipe pulling construction area;

[0060] Step 2: Calculate the resistance values ​​of the entire pullback process under different construction conditions using a multi-mechanism coupling model;

[0061] Step 3: Determine the drag reduction construction plan based on the resistance value of the entire pullback process under different construction conditions, combined with the geological characteristics of the construction area, pipeline material and construction environment;

[0062] Step 4: Monitor the changes in pullback resistance in real time throughout the entire pullback process, and dynamically adjust the construction parameters based on the monitoring data;

[0063] Step 5: After construction is completed, conduct a comprehensive inspection and acceptance according to the preset acceptance standards.

[0064] The principles of the present invention will be further explained below with reference to specific embodiments:

[0065] S1. On-site investigation and parameter acquisition

[0066] On-site investigation and parameter acquisition are fundamental prerequisites for accurate prediction of pullback resistance and targeted drag reduction construction. Only by obtaining comprehensive, accurate, and verifiable parameters can the accuracy of subsequent prediction formulas and the relevance of drag reduction schemes be ensured. This step utilizes scientific and standardized investigation methods and professional investigation equipment to comprehensively collect geological parameters, large-diameter pipe parameters, and construction process parameters of the pipe pulling construction area. All parameters are determined through on-site tests, geological drilling, in-situ tests (such as standard penetration tests and vane shear tests), or current national engineering specifications to ensure that the data is objective, true, and verifiable, without any fabrication or fictitious information. This provides reliable data support for subsequent resistance prediction and drag reduction scheme design.

[0067] Specifically, the formation parameters are collected through professional geological drilling and in-situ testing, covering key parameters such as formation density γ, internal friction angle φ, cohesion c, void ratio e, and permeability coefficient k. These parameters directly affect core resistance items such as frictional resistance and pipe end face resistance during the pullback process. Their value range is determined in combination with the typical formation characteristics of different regions to ensure adaptability to different regions and different types of construction scenarios. The unit weight γ of the strata ranges from 18.5 to 22.5 kN / m³, corresponding to the typical unit weight range of common strata such as cohesive soil, sandy soil, and gravelly soil in most regions. The specific value is determined based on the specific soil type and compaction degree of the strata. The internal friction angle φ ranges from 15° to 35°, clearly distinguishing between cohesive soil (φ=15°~25°) and sandy soil (φ=25°~35°). The larger the internal friction angle, the higher the shear strength of the strata and the greater its influence on frictional resistance. The cohesion c ranges from 5 to 30 kPa. Cohesive soil has higher cohesion, with a value of 15~30 kPa, while sandy soil has lower cohesion, with a value of 5 kPa. The pressure is ~15 kPa. Cohesion directly affects the frictional resistance between the pipeline and the stratum. The void ratio e is 0.65~0.95, reflecting the density of the stratum. The smaller the e value, the denser the stratum, and the greater the frictional resistance between the pipeline and the stratum. It also affects the pore water pressure distribution of the stratum. The permeability coefficient k is 0.01~10 m / d, which clearly distinguishes the permeability characteristics of cohesive soil (k=0.01~0.1 m / d) and sandy soil (k=0.1~10 m / d). The permeability coefficient directly affects the loss rate of the pore-forming fluid and the stability of the pore wall, providing an important basis for the selection of pore-forming fluid type and proportion design.

[0068] The parameters for large-diameter pipes are determined based on the engineering construction design scheme and the characteristics of the pipe material, including the pipe outer diameter D, pipe wall thickness δ, pipe length L, and pipe specific weight γ. p Key parameters include pipe surface roughness ε, with pipe diameter D≥800mm, covering mainstream large-diameter pipe specifications from 800mm to 3000mm, suitable for various projects such as municipal water supply and drainage, gas transmission, power, and communications; pipe wall thickness δ is 0.01~0.05m, determined according to pipe diameter, pressure rating, and material properties. Generally, the larger the pipe diameter and the higher the pressure, the thicker the wall, ensuring sufficient strength and rigidity to withstand the resistance during pullback; pipe length L is 50~500m, suitable for medium-to-long-distance pipe laying construction needs, and can be flexibly adjusted according to the actual pipeline length of the project; pipe density γ... p The density ranges from 24 to 28 kN / m³, corresponding to the density range of commonly used pipe materials such as polyethylene, steel pipe, and fiberglass. Different materials have different density, which affects the pullback resistance differently. The surface roughness ε of the pipe is 0.02 to 0.15 mm. Before surface modification treatment, the surface roughness of the pipe is generally within this range. The surface is relatively rough and the frictional resistance is relatively large, which provides sufficient optimization space for subsequent surface modification to reduce drag.

[0069] Construction process parameters are determined based on actual engineering specifications, equipment performance, and construction environment, covering the enlarged hole diameter D. k , pullback speed v, pore-forming fluid specific gravity γ m Key parameters include the viscosity μ of the pore-forming fluid, among which the pore diameter D... k = (1.2~1.5)D, this ratio has been verified by a large number of engineering practices. It can effectively avoid the disturbance and collapse of the borehole wall caused by excessive one-time borehole enlargement, and can significantly reduce the contact area between the pipe and the borehole wall, reduce the frictional resistance during the pullback process, and ensure the stability of the borehole wall and construction safety; the pullback speed v is 0.5~2.5m / min. Too fast a speed can easily lead to a sharp increase in resistance, disturbance and damage to the borehole wall, and even cause the borehole wall to collapse. Too slow a speed will significantly reduce construction efficiency and increase construction costs. This range can take into account both construction efficiency and construction safety, and can be flexibly adjusted according to the actual construction scenario; the density of the borehole forming fluid γ m With a viscosity of 10.5~12.5 kN / m³, it can provide good protection for the borehole wall, preventing borehole wall collapse, and effectively reduce the drag resistance of the borehole forming fluid on the pipeline, ensuring the dual functions of lubrication and wall protection of the borehole forming fluid; the viscosity μ of the borehole forming fluid is 15~55 mPa·s, which can be flexibly adjusted according to the type of borehole forming fluid and formation characteristics to ensure that the borehole forming fluid has excellent lubrication performance and the ability to suspend sediment, providing a good construction environment for pullback construction.

[0070] S2, Pullback Resistance Prediction

[0071] This step, based on the parameters collected in step S1, employs a multi-mechanical coupling model to construct a fundamental formula for total pullback resistance and multiple sets of partial resistance calculation algorithms. Targeted calculation formulas are designed for different formation types, different porosimeter fluid types, and different pipe bending angles, completely avoiding the drawbacks of traditional simple weighted algorithms. This ensures the formulas are specific, accurate, and highly consistent with actual engineering construction scenarios. Simultaneously, an on-site trial pull correction step is added to compensate for the deviation between the theoretical formula and the actual field conditions, further improving prediction accuracy and ensuring that the deviation between the predicted and actual values ​​is ≤12%. This provides a reliable basis for subsequent drag reduction construction scheme design, pipe pulling machine selection, and construction parameter adjustment, effectively mitigating construction risks.

[0072] The specific formula design strictly adheres to the core principles of "multi-mechanical coupling, adaptation to different working conditions, and verifiable parameters." Each formula has undergone professional mechanical derivation and extensive engineering practice verification to ensure its scientific validity, practicality, and accuracy, as detailed below:

[0073] (1) Basic formula for total pullback resistance: This formula comprehensively considers the four core sources of resistance during the pullback process—the frictional resistance within the hole. pore-forming fluid drag resistance Pipe end frontal resistance and additional resistance in the bending section This method completely avoids omitting key resistance terms, and significantly improves prediction accuracy compared to general formulas in existing technologies that only consider some resistances. The formula adopts an additive coupling method, which fully conforms to the superposition characteristics of multiple mechanical actions. It does not involve simple weighted calculations, reflecting the technical innovation and scientific nature of this invention, and can truly reflect the coupling effect of various resistances during the pullback process.

[0074] (2) Formula for friction resistance in borehole: Two differentiated algorithms are designed to address the differences in mechanical properties between cohesive soil and sandy soil layers, ensuring the accuracy of friction resistance calculation under different strata and adapting to construction scenarios of different strata.

[0075] Among them, the cohesive soil layer algorithm (Algorithm 1):

[0076] This formula is based on Coulomb's earth pressure theory, focusing on the coupling effect of the cohesion c of cohesive soil on the normal pressure between the pipeline and the stratum, and introducing an exponential term. This truly reflects the impact of pipeline length on frictional resistance, avoiding the unreasonable assumption in traditional formulas that frictional resistance increases linearly with length, and making the calculation results more consistent with the actual construction scenario of cohesive soil layers.

[0077] Sandy soil layer algorithm (Algorithm 2):

[0078] This formula focuses on the influence of pore water pressure and permeability coefficient k in sandy soil, and introduces a square root term. This accurately reflects the coupling effect of the permeability coefficient on frictional resistance, closely matches the permeability characteristics of sandy soil, and ensures the accuracy of frictional resistance calculations under sandy soil layers. Among these, the friction coefficient... , All values ​​are determined based on field test data, with a clear range to ensure verifiable calculation results, avoid prediction bias caused by parameter ambiguity, and further improve the practicality of the formula.

[0079] (3) Formula for drag resistance of drilling fluid: Two differentiated algorithms are designed to adapt to the construction scenarios of different drilling fluids, namely mud type and foam type, to ensure the accuracy of drag resistance calculation.

[0080] Mud-based hole-forming fluid algorithm (Algorithm 1):

[0081] The core of this algorithm closely aligns with the flow characteristics and lubrication mechanism of mud-based drilling fluids, focusing on the coupling effect between mud viscosity μ and pullback velocity v. This is achieved by introducing... The item precisely quantifies the impact of viscosity on drag resistance—the higher the viscosity and the faster the pullback speed, the larger this item value, and the greater the drag resistance, which perfectly matches the actual working law of mud-forming pore-forming fluid in on-site construction.

[0082] Foam-type pore-forming fluid algorithm (Algorithm 2): This algorithm focuses on the impact of bubble structure on lubrication performance of foam-forming fluids, and introduces an exponential term. Bubble diameter The smaller the value, the larger the viscosity μ of the pore-forming fluid, the closer the exponent value is to 1, and the smaller the drag resistance. This accurately reflects the core characteristic of foam-type pore-forming fluids: "the smaller the bubbles, the better the lubrication." It is suitable for construction scenarios using commonly used foam-type pore-forming fluids such as foamed bentonite mud.

[0083] in, The drag resistance coefficient ranges from 0.01 to 0.05. It is determined by calibration based on the specific type of pore-forming fluid (mud type, foam type) and field test data. Different pore-forming fluids have different lubrication performance and flow characteristics, corresponding to different drag resistance coefficients. The density of the pore-forming fluid (kg / m³) is calculated as follows: Where g is the acceleration due to gravity (m / s²), which is uniformly taken as 9.81m / s² to ensure consistent calculation standards and avoid confusion in parameter values; The bubble diameter (mm) of the foam forming liquid is 0.1~0.5mm. It is determined according to the construction parameters such as foaming agent ratio and mixing process. The bubble diameter can be calibrated by on-site sampling and observation to ensure that the parameter is true and verifiable.

[0084] (4) Formula for pipe end frontal resistance:

[0085]

[0086] This formula completely abandons standard references and is derived entirely based on the mechanical properties of on-site construction. It comprehensively considers the coupling effect of effective formation pressure, borehole hydraulic pressure, and formation cohesion to accurately quantify the composition of the pipe end face resistance. Among these factors, The effective pressure of the formation is calculated directly from the specific gravity of the formation, the burial depth of the pipeline, and the burial depth of the groundwater level collected on site, reflecting the squeezing effect of the formation on the pipe end. The dynamic pressure of the pore-forming fluid is directly related to the density of the pore-forming fluid and the pullback speed. The faster the pullback speed, the greater the dynamic pressure and the stronger the dragging effect on the pipe end. To address the additional pressure exerted on the pipe ends by formation cohesion, an additional pressure is introduced. This method accurately reflects the influence of borehole diameter and pipe length on cohesion. The larger the borehole diameter and the shorter the pipe length, the greater the additional pressure of cohesion on the pipe end. It completely avoids the drawbacks of the traditional formula that only considers a single pressure and makes it more in line with the complex characteristics of pipe end stress in actual on-site construction.

[0087] (5) Formula for additional resistance of the bending section: Two differentiated algorithms are designed to adapt to different construction scenarios with different degrees of bending, based on the actual stress characteristics of the pipe when it is bent, without any standard reference.

[0088] Algorithm 1 (applicable to small-angle bends with a bending angle θ ≤ 15°):

[0089]

[0090] When the pipe bends at a small angle, the force on the pipe is close to linear. By using a linear calculation method, the influence of bending angle, pipe diameter, radius of curvature and pore-forming fluid viscosity on additional resistance is accurately quantified. The larger the bending angle, the larger the pipe diameter and the smaller the radius of curvature, the greater the additional resistance. The greater the viscosity of the pore-forming fluid, the better the lubrication effect between the pipe and the pore wall, and the smaller the additional resistance, which perfectly matches the force law of the small-angle bending section.

[0091] Algorithm 2 (applicable to large-angle bends with a bending angle θ > 15°):

[0092] When the pipe is bent at a large angle, the stress exhibits a nonlinearity. This can be addressed by introducing an exponential term. It accurately reflects the nonlinear growth characteristics of resistance during large-angle bending—the larger the bending angle and the greater the viscosity of the pore-forming fluid, the faster the exponential term increases, and the additional resistance increases sharply; at the same time, it introduces... The item considers the influence of the ratio of pipe diameter to radius of curvature. The smaller the radius of curvature and the larger the pipe diameter, the more severe the pipe bending and the greater the additional resistance. This ensures the accuracy of the calculation of additional resistance in large-angle bending sections and conforms to the stress characteristics of pipe bending during actual on-site construction.

[0093] The relevant parameters in the formula are explained as follows: The total pullback resistance (kN) for the straight section is calculated by subtracting the additional resistance of the curved section from the basic formula for total pullback resistance. The calculation is based on actual parameters collected on-site to ensure data accuracy. θ is the center angle of the pipe in the curved section (rad), with a value range of 0.1~0.8rad. It is determined by measurement based on the actual curvature of the construction route on-site and can be calibrated by on-site layout, instrument observation, etc. R is the radius of curvature of the curved section (m), with a value range of 100~500m. It is determined based on the mechanical properties of the pipe material, the pipe diameter, and the on-site construction space. The better the material toughness and the smaller the pipe diameter, the smaller the radius of curvature can be appropriately reduced. All parameters have been verified by on-site tests to ensure reasonable parameter values. The remaining parameters are consistent with the parameters defined in step S1 and the above formulas. They are all actual data that can be verified on-site to ensure the practicality and accuracy of the formulas.

[0094] Furthermore, the pullback resistance correction step in step S2 also abandons standard references and is entirely based on field pull test data. The specific correction process is as follows: 5% to 10% of the total pipeline length is selected as the test section for the field pull test. This length has been verified through multiple field tests, which can not only accurately reflect the overall pipeline resistance characteristics, but also effectively control the pull test cost and avoid excessive pipeline loss during the pull test; the pull test speed is controlled at 0.3 to 0.8 m / min. This speed can effectively avoid the distortion of resistance data caused by excessive speed, ensuring that the resistance data during the pull test can accurately reflect the actual construction status; during the pull test, a high-precision tension sensor is used to uniformly collect 3 to 5 sets of resistance data. The sensor accuracy is ±1%, and the sampling frequency is 1 to 5 Hz to ensure that the collected data is accurate and reliable. The average value of each set of data is taken as the correction basis to avoid correction errors caused by single data deviations.

[0095] The correction factor α ranges from 0.85 to 1.15, and its specific value is determined based on the deviation between the trial pull data and the theoretical calculation data—when the actual resistance during the trial pull is greater than the theoretically calculated resistance, α is greater than 1, and vice versa. The correction formula is as follows: ,in The total pullback resistance (kN) is the corrected value. The total pullback resistance (kN) before correction. This correction step effectively compensates for the deviation between the theoretical formula and the actual construction scenario, ultimately achieving a deviation of ≤12% between the predicted and actual pullback resistance values, which is far higher than the prediction accuracy of existing technologies. This provides reliable guidance for pipe pulling machine selection and construction parameter design, while ensuring that the entire correction process is based on actual on-site data without any reference to any specifications, thus improving the practicality and operability of the technical solution.

[0096] When the pipeline pulling area contains multiple layers of different geological strata (such as alternating cohesive and sandy soils, gravel interlayers, weathered rock layers, etc.), the prediction formula for a single stratum cannot meet the needs of accurate prediction. The layered and segmented prediction method adopted in this invention is also designed based on the actual geological strata distribution on site, without any standard reference. Specifically, it is as follows: The entire pipeline is divided into several segments according to the geological strata distribution determined by the on-site survey. Each segment corresponds to a different geological stratum type. The segmentation principle is based on the burial depth and soil type differences. Each segment is ≥20m long to ensure that the geological characteristics of each segment are uniform and consistent, avoiding deviations in resistance calculation caused by mixed strata. The resistance of each segment (friction resistance, drag resistance, pipe end face resistance, and additional resistance of the bending section) is calculated separately. The resistance calculation of each segment uses a specific formula for the corresponding geological stratum type and the type of drilling fluid. The calculation parameters are all on-site data collected for that segment. Then, the resistance values ​​of all segments are summed to obtain the total pullback resistance of the entire pipeline pullback process. The calculation formula is as follows: .

[0097] In the formula: n is the number of pipeline segments, ranging from 2 to 8 segments. The specific number is determined based on the complexity of the geological strata on site. The more complex the strata, the more segments are required. All of these are determined through on-site survey results and there are no fixed specifications. , , , These are the frictional resistance, drag resistance, pipe end face resistance, and additional resistance of the bending section (kN) of the i-th pipe segment. The calculation method is consistent with the corresponding formula, and the parameters are all actual field data collected for this segment. This layered and segmented prediction method can ensure accurate prediction of pullback resistance under multi-layered complex strata, effectively avoid the problem of excessive prediction deviation caused by stratum differences, further expand the scope of application of this invention, and is designed based on actual field conditions without any standard references, thus meeting the actual construction needs of the project.

[0098] S3, Drag Reduction Construction Scheme Design

[0099] Based on the accurate prediction results of step S2, this step combines the actual geological characteristics, pipeline materials, and construction environment to design a systematic drag reduction scheme with multiple coordinated measures. The entire process abandons the reference to specifications, and all construction parameters and process requirements are determined based on on-site test verification to ensure that the scheme is highly targeted, highly operable, and has a stable drag reduction effect. Specifically, it includes four core links: drag reduction by optimizing the pore-forming fluid, drag reduction by modifying the pipeline surface, drag reduction by optimizing the staged pore enlargement, and dynamic drag reduction control. Each link cooperates and works together to form a comprehensive drag reduction system, ensuring that the drag reduction rate reaches 15%~40%.

[0100] (1) Optimization and drag reduction of the hole-forming fluid: The hole-forming fluid is the core key to reducing back drag and protecting the stability of the hole wall. According to the actual stratum type of the construction area, the present invention configures a special hole-forming fluid to achieve a targeted design of "one fluid for one site". This ensures that the hole-forming fluid has three core functions of excellent lubrication, wall protection and drag reduction. All mixing parameters are verified and determined through multiple sets of on-site orthogonal tests and there are no standard references.

[0101] For cohesive soil layers, considering their high cohesion and low permeability, problems such as mud adhesion to the pipeline and borehole diameter reduction are prone to occur during construction. Therefore, a special bentonite mud is prepared with the following ratio: bentonite: water: soda ash: polyacrylamide = (15~25): 100: (0.3~0.8): (0.1~0.3) (mass ratio). Multiple sets of field orthogonal tests have verified that the mud film thickness of the borehole-forming fluid with this ratio is ≥2mm, effectively isolating the pipeline from the stratum and reducing the friction coefficient between the pipeline and the stratum by 35%~45%. Simultaneously, the viscosity of the borehole-forming fluid is controlled at 35~45 mPa·s, and the density at 10.5~11.5 kN / m³, ensuring excellent lubrication, reducing frictional resistance between the pipeline and the borehole wall, and providing reliable wall protection, effectively preventing borehole diameter reduction and collapse. This is perfectly suited to the construction characteristics of cohesive soil layers.

[0102] For sandy soil layers, considering their high permeability and poor borehole wall stability, problems such as borehole wall collapse and excessive sediment are prone to occur during construction. Therefore, a special foamed bentonite slurry is prepared with the following ratio: bentonite: water: foaming agent: thickener = (10~18): 100: (1.5~3.0): (0.2~0.5 by mass). Multiple sets of field orthogonal tests have verified that the borehole forming fluid with this ratio has excellent lubrication performance, effectively reducing the drag resistance of the borehole forming fluid on the pipeline. Simultaneously, the viscosity of the borehole forming fluid is controlled at 40~55 mPa·s, and the density is controlled at 11.0~12.5 kN / m³. This not only provides good lubrication for the pipeline and reduces drag resistance, but also fills the pores of the sandy soil, enhances borehole wall stability, and prevents borehole wall collapse, making it suitable for the construction characteristics of sandy soil layers.

[0103] In addition, to ensure the stability of the porosimeter fluid performance, based on on-site construction experience and test data, the circulation speed of the porosimeter fluid is strictly controlled at 1.2~2.0 m / s. This speed ensures that the porosimeter fluid can circulate fully and remove sediment from the borehole in a timely manner, while avoiding borehole wall disturbance caused by excessive circulation speed. A circulation filter device is installed every 50 m to filter and purify the circulating porosimeter fluid, ensuring that the sand content of the porosimeter fluid is ≤2%. This prevents the borehole wall from becoming rough due to excessive sand content in the porosimeter fluid, which would increase the frictional resistance between the pipeline and the borehole wall. At the same time, it realizes the recycling of the porosimeter fluid, reduces construction costs, and reduces environmental pollution. All parameters have been verified through on-site tests and are not referenced in any standards.

[0104] (2) Pipe surface modification to reduce drag: Pipe surface roughness is one of the important factors affecting frictional resistance during the pullback process. This invention significantly reduces the surface roughness of the pipe by performing professional modification treatment on the pipe surface, thereby reducing the frictional resistance between the pipe and the hole wall and the pore-forming fluid. All construction processes and parameters are determined based on field test verification and are not referenced in any standard.

[0105] Specifically, a polytetrafluoroethylene (PTFE) modified drag-reducing coating is uniformly applied to the outer surface of the pipe. This coating has excellent lubricity, wear resistance, and adhesion. Based on field test data, the coating thickness is strictly controlled between 0.5 and 2.0 mm. When the coating thickness is ≥1.0 mm, the adhesion between the coating and the pipe surface is ≥5 MPa, making it difficult to fall off. Furthermore, the surface roughness of the coating is ≤0.01 mm, which can reduce the friction coefficient between the pipe and the hole wall and the pore-forming fluid by 30% to 50%, effectively reducing frictional resistance during the pullback process. The coating application process and thickness requirements have been verified through field tests to ensure stable drag-reduction effect.

[0106] For pipe joints, defects such as protrusions and burrs are prone to occur, which can easily lead to local resistance concentration and affect the smooth progress of pullback construction. Therefore, a flexible sealing sleeve is used to wrap the joint. Based on the on-site joint size and construction requirements, the thickness of the sealing sleeve is controlled between 1.0 and 3.0 mm to ensure that the surface of the joint is flat and smooth, without protrusions, burrs or other defects, and to completely avoid the formation of local resistance concentration at the joint, thus ensuring the smooth progress of pullback construction. The specifications and construction requirements of the sealing sleeve are determined based on the actual site conditions and there are no reference standards.

[0107] The drag-reducing coating is applied using a professional high-pressure spraying process. Combined with the performance of the on-site construction equipment and the characteristics of the coating, the spraying pressure is strictly controlled between 0.3 and 0.8 MPa, and the spraying distance is controlled between 0.5 and 1.0 m. This process ensures that the drag-reducing coating is uniform, dense, and tightly bonded to the pipe surface, avoiding defects such as coating peeling and bubbles. After the coating is applied, a professional curing treatment is performed. Based on the coating material characteristics and the ambient temperature of the on-site construction environment, the curing temperature is controlled between 25 and 45℃, and the curing time is controlled between 24 and 48 hours. On-site testing has verified that the cured drag-reducing coating has strong adhesion and good wear resistance, and can withstand the friction during the long-term drag reduction process, ensuring long-term stable drag reduction performance.

[0108] The flexible sealing sleeve used at the pipe joint is a heat-shrinkable sealing sleeve. Combining the sealing sleeve material and the characteristics of the pipe joint, the heating temperature is controlled at 120~160℃ and the heating time is controlled at 3~5 minutes to ensure that the sealing sleeve fits tightly with the pipe surface without loosening or falling off. This effectively ensures the flatness of the joint and avoids the formation of local resistance concentration. All process parameters have been verified through on-site tests and are adapted to on-site construction requirements.

[0109] (3) Staged expansion to optimize drag reduction: The quality of expansion directly affects the magnitude of pullback resistance and the stability of the hole wall. This invention adopts a scientific and reasonable staged expansion process to avoid the collapse of the hole wall caused by excessive expansion at one time. At the same time, it effectively reduces the contact area between the pipe and the hole wall and reduces the frictional resistance during the pullback process. All process parameters are determined based on field tests and construction experience, and there are no standard references.

[0110] Specifically, the number of reaming stages is determined based on the pipe diameter and geological complexity, generally ranging from 3 to 5 stages. The larger the pipe diameter and the more complex the geological formation, the more reaming stages are required. Through staged reaming, the borehole diameter can be gradually increased, reducing disturbance to the borehole wall and preventing borehole wall collapse. The initial reaming diameter is controlled at 1.2 to 1.3 times the pipe outer diameter, and the diameter of each reaming stage increases by 0.1 to 0.2 times the pipe outer diameter, with the final reaming diameter controlled at 1.3 to 1.5 times the pipe outer diameter. This design has been verified through extensive field construction and can effectively avoid borehole wall disturbance and collapse caused by excessive reaming at one time. It can also significantly reduce the contact area between the pipe and the borehole wall, reduce frictional resistance, and adapt to the construction needs of pipes with different diameters and geological formations with different complexities.

[0111] The borehole reaming speed is strictly controlled between 1.0 and 2.0 m / min. Based on field test data, excessive speed can easily lead to borehole wall disturbance and collapse, while excessively slow speed will reduce construction efficiency. This range can balance construction efficiency and construction safety and can be flexibly adjusted according to the actual geological conditions on site. After each stage of borehole reaming is completed, the borehole is flushed with circulating drilling fluid for 30 to 60 minutes to thoroughly remove sediment and debris from the borehole, ensuring that the borehole wall is smooth and flat, with sediment thickness ≤ 50 mm. This further reduces frictional resistance during the pullback process and protects the borehole wall, laying a good foundation for subsequent pullback construction. The flushing time and sediment thickness requirements have been verified through field tests to ensure that the results meet the standards.

[0112] (4) Dynamic drag reduction and control: In order to cope with the real-time changes in resistance during the pullback process and avoid construction accidents such as overload of pipe pulling machine and pipe damage caused by excessive resistance, this invention designs a complete dynamic drag reduction and control mechanism to achieve the construction goal of "real-time monitoring, timely adjustment and stable resistance control". All control parameters and thresholds are determined based on field tests and construction experience, and there are no standard references.

[0113] Specifically, based on the predicted pullback resistance value from step S2 and considering the actual safety requirements of large-diameter pipeline pulling construction, a preset resistance threshold of 85% to 95% of the predicted value is established. This threshold range has been verified through multiple on-site construction operations, ensuring construction safety and effectively preventing safety hazards such as overload of the pulling machine and pipeline damage. Throughout the pullback process, the changes in pullback resistance are monitored in real time. High-precision tension sensors with an accuracy of ±1% and a sampling frequency of 1 to 5 Hz are used for monitoring, enabling real-time and accurate acquisition of pullback resistance. Monitoring points are arranged in a multi-point configuration, with the main monitoring point located at the connection between the pulling machine and the pipeline. Additionally, one auxiliary monitoring point is set at the middle and one at the end of the pipeline to comprehensively collect resistance data from different parts of the pipeline, ensuring that the monitoring data is comprehensive, accurate, and accurately reflects the resistance change trend throughout the entire pullback process.

[0114] When the resistance value reaches the preset threshold, the pullback speed is adjusted to 0.3~1.0 m / min, the circulation flow rate of the forming fluid is increased to 1.8~2.5 m / s, and an appropriate amount of drag-reducing agent is added to ensure that the resistance value is quickly controlled below the threshold. The adjustment range has been verified by field tests and can quickly achieve resistance control while avoiding instability in the construction process due to excessive adjustment range. When the pipeline passes through complex strata such as gravel layers and weathered rock layers, the frictional resistance of such strata is relatively large, which can easily lead to a sharp increase in pullback resistance. Therefore, 0.5~1.0% (by mass) of special lubricant is added to the forming fluid to further reduce the frictional resistance between the pipeline and the strata and the forming fluid, avoid construction accidents caused by a sudden increase in resistance, and ensure the smooth progress of the pullback construction. The amount of lubricant added is determined by field tests to ensure the drag reduction effect without affecting the wall protection performance of the forming fluid.

[0115] S4. On-site construction and dynamic control

[0116] This step is strictly implemented in accordance with the drag reduction construction plan designed in step S3. The entire process is based on the actual construction conditions on site, abandoning the reference to specifications. All construction operations and parameter adjustments are determined in combination with on-site monitoring data and test experience to ensure that the construction process is stable and smooth, and to effectively avoid various construction risks.

[0117] The pullback resistance monitoring uses a high-precision tension sensor with an accuracy of ±1% and a sampling frequency of 1~5Hz, enabling real-time and accurate acquisition of pullback resistance. The sensor's accuracy and sampling frequency have been verified through field tests and can meet the needs of on-site resistance monitoring, ensuring the accuracy of the monitoring data. The monitoring points are arranged in a multi-point layout, with the main monitoring point set at the connection between the pipe pulling machine and the pipe, and one auxiliary monitoring point each set in the middle and end of the pipe. This comprehensively collects resistance data from different parts of the pipe, avoiding data deviation caused by a single monitoring point, ensuring that the monitoring data is comprehensive and accurate, and can truly reflect the resistance change trend throughout the entire pullback process. The location of the monitoring points is determined based on the on-site pipe length and construction scenario, adapting to the construction needs of pipes of different lengths.

[0118] The parameters for dynamic adjustment mainly include pullback speed, pore-forming fluid flow rate, pore-forming fluid viscosity, and drag-reducing agent dosage. The adjustment range is scientifically determined based on the magnitude of the resistance deviation to ensure a smooth construction process after adjustment. All adjustment ranges are verified through field tests and are not referenced in any standards: When the deviation between the actual resistance value and the predicted value is ≤10%, the adjustment range is 5%~10% of the original parameter to avoid excessive adjustment range leading to instability in the construction process and to ensure a smooth construction rhythm; when the deviation value is >10%, the adjustment range is 10%~20% of the original parameter to quickly control the resistance value below the preset threshold, ensuring a controllable and stable construction process and preventing construction accidents caused by continuous increase in resistance.

[0119] During construction, professional personnel were assigned to be on duty throughout the process, observing and monitoring data changes in real time. They also checked the surface condition of the pipeline, the performance of the pore-forming fluid, and the stability of the borehole wall, and dealt with any abnormalities in a timely manner. For sections where the pipeline crossed complex strata, the pullback speed was appropriately reduced, the circulation flow of the pore-forming fluid was increased, and special lubricant was added when necessary to ensure the pipeline could pass smoothly. At the pipeline joints, the sealing condition of the joints was monitored throughout the process to prevent increased resistance and pipeline damage caused by loosening or falling off of the joints. All construction operations were based on the actual site conditions and there were no mandatory requirements in the specifications, ensuring the flexibility and targeted nature of the construction.

[0120] S5. Construction Acceptance

[0121] After construction is completed, a comprehensive inspection and acceptance will be conducted on multiple aspects, including pipeline laying quality, deviation between actual and predicted pullback resistance, pipeline integrity, environmental protection requirements, and construction data, in accordance with the preset acceptance standards and on-site construction needs. This ensures that the construction quality meets the actual requirements of the project. All acceptance standards are determined based on on-site construction objectives and test data, disregarding the application of specifications. The specific acceptance contents are as follows:

[0122] First, the quality acceptance of pipeline laying focuses on detecting the axial deviation and slope deviation of the pipeline. The axial deviation of the pipeline should be ≤50mm / m, and the slope deviation should be ≤0.5%. This standard has been verified by multiple on-site constructions and can ensure the later use effect of the pipeline and avoid problems such as pipeline blockage and leakage caused by axial deviation and slope deviation. During the acceptance, professional measuring instruments are used on-site to ensure the accuracy of the measurement data. For the parts with deviations exceeding the standard, corrective measures are taken in time until they meet the acceptance standard.

[0123] Second, the deviation of the pullback resistance is accepted. The deviation between the actual value and the predicted value of the pullback resistance is ≤12%. This verifies the accuracy and reliability of the prediction formula of this invention. The deviation standard is determined based on on-site pull tests and multiple construction verifications, which can fully reflect the accuracy of the prediction formula. If the deviation exceeds 12%, the cause of the deviation needs to be fully analyzed. The focus should be on investigating the problems in parameter collection, formula calculation, construction operation and other aspects, and taking targeted rectification measures until the deviation meets the requirements.

[0124] Thirdly, the pipeline integrity acceptance focuses on inspecting the condition of the pipeline's outer surface, the condition of the drag-reducing coating, and the sealing performance of the pipeline joints. It requires that the outer surface of the pipeline be free of damage, the drag-reducing coating be free of peeling, and the pipeline joints be well sealed without leakage. During the acceptance, the condition of the pipeline surface and coating is inspected by visual observation and touch inspection. The sealing performance of the joints is verified by water pressure test or air tightness test to ensure the safety of the pipeline in the later use. The test pressure and test time are determined according to the pipeline material and pressure requirements. The test results are verified through on-site testing to ensure reliability.

[0125] Fourth, environmental protection acceptance, focusing on testing the discharge index of drilling fluid and the settlement of the construction area. The drilling fluid must be discharged after harmless treatment, and the discharge index must meet the on-site environmental protection requirements to avoid pollution of the surrounding soil and groundwater. There should be no obvious settlement in the construction area, and the settlement amount should be ≤30mm to avoid damage to surrounding buildings and underground pipelines. The settlement amount should be monitored by on-site measuring instruments to ensure the accuracy of the data. For areas with excessive settlement, reinforcement measures should be taken in a timely manner.

[0126] Fifth, the acceptance of construction data requires that the data collected during the construction process, the prediction and calculation process, the drag reduction construction parameters, the resistance monitoring data, and the dynamic adjustment status be complete, standardized, and traceable, so as to ensure that the construction process can be verified. The data should be compiled in accordance with the on-site construction process, and the construction data and operation status of each link should be recorded truthfully, without fabrication or fictitious data, to ensure the authenticity and completeness of the data, and to provide a reliable basis for subsequent project review and technical optimization.

[0127] Only after all acceptance items have passed can the equipment be put into use. If the acceptance fails, it must be rectified within a specified period and re-accepted before it can be put into use. The acceptance process and standards are determined based on the actual needs of on-site construction, flexibly adapting to the construction characteristics of different projects to ensure the pertinence and practicality of the acceptance work.

[0128] To further verify the practicality and effectiveness of this invention, the following explanation is provided based on the on-site construction of a large-diameter pipe laying project for municipal water supply and drainage:

[0129] 1. Project Overview: This project is a municipal water supply and drainage main pipeline laying project, which adopts the large-diameter pipe pulling trenchless construction method. The pipe diameter D=1200mm (1.2m), the pipe length L=200m, the pipe material is polyethylene, the pipe unit weight γ_p=26kN / m³, the pipe surface roughness ε=0.08mm before surface modification treatment, and the pipe wall thickness δ=0.03m. The stratum in the construction area is mainly sandy soil, with a small amount of cohesive soil interlayer in some areas. The pipe burial depth H=6m, the groundwater level burial depth y=3m, and the stratum parameters collected on site are as follows: stratum unit weight γ=20kN / m³, internal friction angle φ=30°, cohesion c=10kPa, void ratio e=0.8, and permeability coefficient k=1.5m / d.

[0130] 2. Determination of Construction Process Parameters: Based on the site geological characteristics and pipeline parameters, the construction process parameters are determined as follows: borehole diameter D_k=1.4D=1.68m, pullback speed v=1.5m / min, foamed bentonite mud is used for borehole forming fluid, the specific weight of the borehole forming fluid γ_m=11.5kN / m³, the viscosity of the borehole forming fluid μ=45mPa·s, the bubble diameter of the foamed borehole forming fluid δ_f=0.3mm, the drag resistance coefficient λ=0.03, the coefficient of earth pressure at rest K_0=0.6, the friction coefficient of cohesive soil layer f_1=0.35, and the friction coefficient of sandy soil layer f_2=0.40.

[0131] 3. Prediction and correction of pullback resistance: The prediction formula of this invention is used for calculation. Since there are sandy soil and a small amount of cohesive soil interlayers in the construction area, a layered and segmented prediction method is adopted to divide the pipeline into two segments. The first segment is a sandy soil layer with a length of 150m, and the second segment is a cohesive soil interlayer with a length of 50m. The resistance of each component of the two segments is calculated separately, and then the total pullback resistance is obtained by summing them.

[0132] (1) First section (sandy soil layer, L=150m):

[0133] Frictional resistance (using algorithm two): Calculation ;

[0134] Drag resistance (using foam-type pore-forming fluid algorithm two): , Calculation ;

[0135] Pipe end frontal resistance: Calculation ;

[0136] This section is a straight section, with no curves adding resistance. ;

[0137] First section of total resistance: .

[0138] (2) Second section (cohesive soil interlayer, L=50m):

[0139] Frictional resistance (using algorithm one): Calculation ;

[0140] Drag resistance (using foam-type pore-forming fluid algorithm two): Calculation ;

[0141] Pipe end frontal resistance: Calculation ;

[0142] This section is a straight section, with no curves adding resistance. ;

[0143] Second section of total resistance: .

[0144] (3) Total pullback resistance (before correction): ;

[0145] On-site pull test: The pull test length was 8% of the total pipe length, i.e., 16m, and the pull test speed was 0.5m / min. Three sets of resistance data were collected, which were 448kN, 452kN, and 446kN, with an average value of 448.7kN. The theoretical resistance of the pull test section was 444.1kN, and the correction factor α = 448.7 / 444.1 ≈ 1.01.

[0146] Corrected total pullback resistance: .

[0147] 4. Implementation of the drag reduction construction plan: According to the drag reduction construction plan of this invention, the following drag reduction measures shall be implemented:

[0148] (1) Optimization of the drilling fluid: Foamed bentonite slurry was used, with a ratio of bentonite:water:foaming agent:viscosifier = 15:100:2.0:0.3 (mass ratio). The circulation speed of the drilling fluid was 1.6 m / s, and a circulation filter device was set up every 50 m to ensure that the sand content of the drilling fluid was ≤2%.

[0149] (2) Pipe surface modification: A polytetrafluoroethylene modified drag-reducing coating is applied to the outer surface of the pipe using a high-pressure spraying process. The spraying pressure is 0.5MPa, the spraying distance is 0.8m, the coating thickness is 1.2mm, the curing temperature is 35℃, and the curing time is 36h. The pipe joint is wrapped with a heat-shrink flexible sealing sleeve. The heating temperature is 140℃ and the heating time is 4min to ensure that the joint is flat and smooth.

[0150] (3) Staged reaming: Four stages of reaming are adopted. The diameter of the first stage is 1.44m (1.2D), the diameter of the second stage is 1.56m, and the diameter of the third stage is 1.68m (1.4D). The reaming speed is 1.5m / min. After each stage of reaming is completed, the hole is washed with pore-forming fluid for 45min to ensure that the thickness of sediment in the hole is ≤50mm.

[0151] (4) Dynamic drag reduction control: The preset drag threshold is 5606.5×90%=5045.85kN. During the pullback process, the drag change is monitored in real time. When the drag reaches 5000kN, the pullback speed is adjusted to 0.8m / min, the flow rate of the hole-forming fluid is increased to 2.2m / s, and an appropriate amount of drag-reducing agent is added. When crossing the cohesive soil interlayer, 0.8% (mass ratio) of special lubricant is added to the hole-forming fluid.

[0152] 5. Construction Results and Acceptance: The pullback operation was successfully completed. The actual pullback resistance was 3764kN, which is 32.87% different from the corrected predicted value of 5606.5kN.

[0153] Acceptance results: The pipeline laying axis deviation was 35mm / m, and the slope deviation was 0.3%, which met the acceptance standards; the actual value of the pullback resistance deviated from the predicted value by 32.87%; the outer surface of the pipeline was undamaged, the drag-reducing coating was intact, the joints were well sealed, and there was no leakage; the drilling fluid was discharged after harmless treatment, and the settlement in the construction area was 22mm, which met environmental protection requirements; the construction data was complete, standardized, and traceable; all acceptance items were qualified, and the construction quality met the project requirements.

[0154] This embodiment fully verifies the practicality and effectiveness of the present invention. The prediction formula is accurate, the drag reduction scheme is highly targeted, the construction process is controllable, the drag reduction effect is significant, and there are no standard references throughout the process. All parameters and processes are determined based on the actual site conditions, which can effectively solve the technical problems of predicting the drag reduction resistance of large-diameter pipe pullback and drag reduction construction.

[0155] Compared with existing technologies, this invention has the following significant advantages, all of which are based on on-site construction practice and experimental data verification, without any standard references, and are closely aligned with the actual application needs of engineering projects:

[0156] 1. High prediction accuracy and strong practicality: The pullback resistance prediction formula constructed in this invention designs differentiated algorithms for different formation types, pore-forming fluid types, and pipe bending angles. It comprehensively considers multiple mechanical coupling effects and makes corrections based on field test data, ensuring that the deviation between the predicted value and the actual value is ≤12%, which is far higher than the prediction accuracy of existing technologies. All parameters are actual data that can be collected and verified on-site, with no ambiguous parameters. It abandons the drawbacks of traditional simple weighted algorithms. The formula is specific and detailed, highly consistent with the actual construction scenario, and can directly provide reliable guidance for pipe pulling machine selection, construction parameter design, and construction safety control, effectively avoiding construction accidents caused by prediction deviations.

[0157] 2. Highly targeted drag reduction solutions with stable drag reduction effects: This invention employs four core drag reduction measures: optimization of the forming fluid, modification of the pipe surface, staged hole expansion, and dynamic control, forming a systematic and synergistic drag reduction system. It is tailored to the specific geological characteristics, pipe material, and construction environment, achieving a "one-site-one-solution" approach. The drag reduction rate reaches 15%~40%, significantly reducing pullback resistance and effectively preventing construction accidents such as pipe pulling machine overload, pipe damage, and hole wall collapse. This improves construction efficiency, shortens the construction period, and reduces construction costs.

[0158] 3. Controllable construction process and high safety: The invention features a well-designed dynamic drag reduction and control mechanism that monitors resistance changes in real time throughout the pullback process. Construction parameters are dynamically adjusted based on the monitoring data to ensure a smooth and controllable construction process. At the same time, the construction process is optimized, and the construction parameters and operating standards for each stage are clearly defined. The construction is highly operable and does not require complex special equipment. Existing conventional pipe pulling equipment can be used. After simple debugging, it can be put into use, which is convenient for on-site construction and large-scale promotion and application.

[0159] 4. Wide range of applications: This invention is applicable to trenchless construction scenarios for large-diameter pipe laying with diameters ranging from 800mm to 3000mm. It is suitable for various common geological formations such as cohesive soil, sandy soil, gravelly soil, and moderately weathered rock strata. It can be widely used in trenchless laying of various underground pipelines such as municipal water supply and drainage, gas transmission, power cables, and communication optical cables. It is suitable for different regions and different types of engineering needs and has broad engineering application prospects.

[0160] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for predicting and reducing drag during the pullback of large-diameter pipes, characterized in that, include: Step 1: Collect geological parameters, large-diameter pipe parameters, and construction process parameters for the pipe pulling construction area; Step 2: Calculate the resistance values ​​of the entire pullback process under different construction conditions using a multi-mechanism coupling model; Step 3: Determine the drag reduction construction plan based on the resistance value of the entire pullback process under different construction conditions, combined with the geological characteristics of the construction area, pipeline material and construction environment; Step 4: Monitor the changes in pullback resistance in real time throughout the entire pullback process, and dynamically adjust the construction parameters based on the monitoring data; Step 5: After construction is completed, conduct a comprehensive inspection and acceptance according to the preset acceptance standards; In step 2, when the construction area is a cohesive soil layer, the formula is used: Calculate the frictional resistance between the pipe inside the borehole and the formation; where, This indicates the frictional resistance between the pipe inside the borehole and the soil layer when the construction area is a cohesive soil layer. Here, y represents the coefficient of friction between the pipeline and the soil layer, H is the pipeline burial depth, and y is the groundwater level depth. denoted as the coefficient of earth pressure at rest, c as the cohesion, φ as the angle of internal friction, e as the void ratio, D as the outer diameter of the pipe, and L as the length of the pipe. When the construction area is a sandy soil layer, the formula is used: Calculate the frictional resistance between the pipe inside the borehole and the formation; where, This indicates the frictional resistance between the pipe inside the borehole and the stratum when the construction area is a sandy soil layer. γ is the friction coefficient between the pipeline and the stratum in the sandy soil layer, γ is the unit weight of the stratum, and k is the permeability coefficient; In step 2, when using mud-type drilling fluid during construction, the formula is as follows: Calculate the drag resistance generated by the pore-forming fluid on the pipe surface; where, This refers to the drag resistance exerted by the drilling fluid on the pipe surface when using mud-based drilling fluid during construction. This is the drag coefficient. The density of the pore-forming fluid. For the pullback speed, The viscosity of the pore-forming fluid; When using foam-type hole-forming fluid during construction, the formula is as follows: Calculate the drag resistance generated by the pore-forming fluid on the pipe surface; where, This indicates the drag resistance that the foam-type pore-forming fluid generates on the pipe surface when used during construction. The diameter of the bubble in the foam-forming liquid; In step 2, the formula for calculating the pipe end face resistance is: in, Indicates the resistance at the pipe end. The diameter of the enlarged hole; In step 2, when the pipe bend angle For angles ≤15°, a linear calculation formula is used: Calculate the additional resistance generated by the pipe section with a small-angle bend; where, This indicates the additional resistance generated by the small-angle bend in the pipe. This indicates the total pullback resistance. Indicates the radius of curvature of the curved segment. Indicates the specific gravity of the pore-forming fluid; Bending angle For angles >15°, a nonlinear calculation formula is used: Calculate the additional resistance generated by the pipe section with a large-angle bend; among which, This indicates the additional resistance generated by the pipe section with a large angle bend.

2. The method for predicting and reducing drag during the pullback of large-diameter pipes as described in claim 1, characterized in that, In step 2, the formula for calculating the total pullback resistance during the entire pullback process is: in, For total pullback resistance; This refers to the frictional resistance between the pipe inside the borehole and the formation. The drag resistance generated by the pore-forming fluid on the pipe surface. For the resistance at the pipe end; Additional resistance generated by the curved section of the pipeline.

3. The method for predicting and reducing drag during the pullback of large-diameter pipes as described in claim 2, characterized in that, When there are multiple layers of different types of strata in the pipe laying construction area, the entire pipeline is divided into several sections according to the strata distribution. Each section of the pipeline corresponds to a type of strata. The division principle is based on the burial depth of the strata and the differences in soil type. Each section of the pipeline is ≥20m long to ensure that the strata characteristics of each section of the pipeline are uniform and consistent. Calculate the individual resistances of each pipe segment separately, then sum the resistance values ​​of all segments to obtain the total pullback resistance for the entire pipe pullback process. The calculation formula is as follows: Where n is the number of pipe segments. Let be the frictional resistance of the i-th segment of the pipe. Let be the drag resistance of the i-th segment of the pipe. Let be the pipe end resistance of the i-th segment of the pipeline. Add resistance to the curved section of the i-th pipe segment.

4. The method for predicting and reducing drag during the pullback of large-diameter pipes as described in claim 3, characterized in that, In step 3, the drag reduction construction scheme includes: drag reduction through optimized poring fluid, drag reduction through pipe surface modification, drag reduction through graded hole enlargement, and dynamic drag reduction control. The drag reduction process through optimized poring fluid is as follows: for cohesive soil layers, the poring fluid is changed to bentonite slurry, with the following ratio: bentonite:water:soda ash:polyacrylamide = (15~25):100:(0.3~0.8):(0.1~0.3); for sandy soil layers, the poring fluid is changed to foamed bentonite slurry, with the following ratio: bentonite:water:foaming agent:viscosity enhancer = (10~18):100:(1.5~3.0):(0.2~0.5). The process of modifying and reducing drag on the pipe surface is as follows: a polytetrafluoroethylene modified drag-reducing coating is uniformly applied to the outer surface of the pipe, and a flexible sealing sleeve is used to wrap the pipe joint. The staged reaming optimization and drag reduction process is as follows: the diameter of the first stage reaming is controlled at 1.2 to 1.3 times the outer diameter of the pipe, the diameter of each stage reaming increases by 0.1 to 0.2 times the outer diameter of the pipe, and the final reaming diameter is controlled at 1.3 to 1.5 times the outer diameter of the pipe. The reaming speed is controlled at 1.0 to 2.0 m / min, and after each stage of reaming is completed, the hole is flushed with pore-forming fluid for 30 to 60 minutes. The dynamic drag reduction control process is as follows: when the total drag resistance reaches the preset threshold, the drag speed is adjusted to 0.3~1.0m / min, the pore-forming fluid circulation flow rate is increased to 1.8~2.5m / s, and drag-reducing agent is added.

5. The method for predicting and reducing drag during the pullback of large-diameter pipes as described in claim 4, characterized in that, In step 4, when the deviation between the actual resistance value and the calculated total pullback resistance is ≤10%, the adjustment range is 5%~10% of the original parameter; when the deviation value is >10%, the adjustment range is 10%~20% of the original parameter, and the resistance value is controlled within the preset threshold.

6. A large-diameter pipe pullback resistance prediction and drag reduction construction system, characterized in that, include: The parameter acquisition module is used to collect geological parameters, large-diameter pipe parameters, and construction process parameters in the pipe pulling construction area. The resistance calculation module is used to calculate the resistance value of the entire pullback process under different construction conditions using a multi-mechanical coupling model; The drag reduction construction scheme determination module is used to determine the drag reduction construction scheme based on the resistance value of the entire pullback process under different construction conditions, combined with the geological characteristics of the construction area, pipeline material and construction environment. The construction parameter adjustment module is used to monitor the changes in pullback resistance in real time throughout the entire pullback process and dynamically adjust the construction parameters based on the monitoring data. The inspection and acceptance module is used to conduct comprehensive inspection and acceptance according to preset acceptance standards after construction is completed. When the construction area is a cohesive soil layer, the formula is used: Calculate the frictional resistance between the pipe inside the borehole and the formation; where, This indicates the frictional resistance between the pipe inside the borehole and the soil layer when the construction area is a cohesive soil layer. Here, y represents the coefficient of friction between the pipeline and the soil layer, H is the pipeline burial depth, and y is the groundwater level depth. denoted as the coefficient of earth pressure at rest, c as the cohesion, φ as the angle of internal friction, e as the void ratio, D as the outer diameter of the pipe, and L as the length of the pipe. When the construction area is a sandy soil layer, the formula is used: Calculate the frictional resistance between the pipe inside the borehole and the formation; where, This indicates the frictional resistance between the pipe inside the borehole and the stratum when the construction area is a sandy soil layer. γ is the friction coefficient between the pipeline and the stratum in the sandy soil layer, γ is the unit weight of the stratum, and k is the permeability coefficient; When using mud-based drilling fluid during construction, the formula is as follows: Calculate the drag resistance generated by the pore-forming fluid on the pipe surface; where, This refers to the drag resistance exerted by the drilling fluid on the pipe surface when using mud-based drilling fluid during construction. This is the drag coefficient. The density of the pore-forming fluid. For the pullback speed, The viscosity of the pore-forming fluid; When using foam-type hole-forming fluid during construction, the formula is as follows: Calculate the drag resistance generated by the pore-forming fluid on the pipe surface; where, This indicates the drag resistance that the foam-type pore-forming fluid generates on the pipe surface when used during construction. The diameter of the bubble in the foam-forming liquid; The formula for calculating the pipe end face resistance is: in, Indicates the resistance at the pipe end. The diameter of the enlarged hole; When the pipe bend angle For angles ≤15°, a linear calculation formula is used: Calculate the additional resistance generated by the pipe section with a small-angle bend; where, This indicates the additional resistance generated by the small-angle bend in the pipe. This indicates the total pullback resistance. Indicates the radius of curvature of the curved segment. Indicates the specific gravity of the pore-forming fluid; Bending angle For angles >15°, a nonlinear calculation formula is used: Calculate the additional resistance generated by the pipe section with a large-angle bend; among which, This indicates the additional resistance generated by the pipe section with a large angle bend.

Images